Vertical cavity lasers work by having a quantum well sandwiched between alternating layers of gallium arsenide (GaAs) and aluminium gallium arsenide (AlGaAs). As the two materials have different refractive indices, the layer stacks act as a set of mirrors that form a resonant cavity. Light from the lasing action is therefore emitted vertically from the […]
The technique works because two different ions, gadolinium and europium, are in the phosphor material. The UV light boosts a gadolinium ion to its excited state. This excess energy is then transferred to two europium ions, both of which emit one photon of red visible light as they drop back down to the ground state. […]
Scientific publishing is still a highly profitable business. According to Nature, the scientific side of the Reed-Elsevier publishing company made a profit of $378m on sales of $938m in 1997. However, the growth of electronic preprint or “eprint” servers, such as the physics server at Los Alamos, will soon radically change the way researchers publish […]
Many biologists have argued that most species become extinct when new ‘fitter’ competitors arrive on the scene. For example, some scientists believe the dinosaurs became extinct after a large meteorite hit the Earth 65 million years ago because warm-blooded mammals were better able to survive the long cold spells that followed. However, palaeontologists now argue […]
Mars is now a dry planet with most of its water either tied up in a deep permafrost or lost to outer space. However, images gathered by Mars Observer and earlier space craft such as the Viking orbiters, showed evidence of water channels, rivers, and water erosion. The most striking evidence consists of wide enormous […]
Quasicrystals are materials that do not have a periodic lattice structure but still display subtle long-range order, such as “five-fold” symmetry, that is not possible in regular crystals. They appear to be built from two different structures assembled in a non-repeating array. Five-fold symmetry was considered impossible in real materials until it was discovered by […]
The world-wide patent rights have been licensed by the university to Nanovation Technologies in Florida. The company hopes to develop an optical circuit which would contain thousands of microcavity lasers on a single semiconductor chip. Tests carried out by the company at Northwestern suggest that such a chip could increase the speed and information capacity […]
James Kikkawa and David Awschalom of the University of California, Santa Barbara have now shown that they can use electric fields to transport electrons through a distance of 0.1 mm in gallium arsenide without losing any of their quantum coherence (Nature 397 139). They cooled gallium arsenide substrates in a magneto-optical cryostat to 1.6 Kelvin. […]
In theory, the creation of ozone – caused by the breakdown of oxygen in the atmosphere by ultraviolet light – is a mass-independent process. However, experiments by Klaus Mauersberger and colleagues at the Max-Planck institute for nuclear physics in Heidelberg indicate that the collisions between oxygen atoms and molecules that form ozone are not mass-independent […]
